Transforaminal Approach

The endoscopic transforaminal approach ( Fig. 1 ) is a uniportal method used in endoscopic spine surgery (ESS) to access the intervertebral disc space through Kambin’s Triangle in the lumbar and thoracic spine. This approach can be used for the initial treatment of foraminal disc herniations and foraminal stenosis successfully. The anatomic limitations to this approach include the superior articulating process, pedicle, and the exiting nerve root and varies at each spinal level and with different pathologies.

Depiction of the foraminal anatomy involved in an endoscopic transforaminal approach.

Lumbar Interlaminar Approach

The endoscopic interlaminar approach ( Fig. 2 ) uses a traditional posterior approach and provides flexibility to an endoscopic spine surgeons repertoire. This technique is primarily used for L5/S1 discectomies due to the anatomic constraints of the iliac crest with a transforaminal approach at that level. It is also used to perform central and lateral recess canal stenosis decompression via laminectomies. A 2018 meta-analysis reported better clinical results with interlaminar endoscopic lumbar discectomy than transforaminal endoscopic lumbar discectomy for L5/S1 disc herniations. The procedure also allows the option for simple conversion to an open operation if needed.

Illustration of the lumbar interlaminar approach.

Cervical Spine Approach

Endoscopic techniques can be used to address both anterior and posterior cervical pathology with minimal spinal cord manipulation and muscle dissection. Endoscopic posterior cervical foraminotomy ( Fig. 3 ) is performed for lateral and foraminal disc herniations and has a high success rate of radiculopathy resolution without serious surgical complications. Endoscopic visualization also allows a posterior view of the intervertebral disc not normally seen with conventional approaches. After the foraminotomy is performed, the nerve root can be manipulated and the foraminal disc herniation removed.

Illustration of the posterior cervical foraminotomy approach.

Full endoscopic and biportal bilateral decompression for cervical stenosis has been described. Carr and colleagues reported their first 10 cases with the technique and demonstrated improvement in postoperative Nurick grades and modified Japanese Orthopedic Association scores without any permanent neurologic complications. ^,

Full endoscopic anterior cervical discectomy without fusion in select patients with soft disc herniations, unilateral radiculopathy and central disc herniations has demonstrated good clinical outcomes. This has been shown to have comparable results to a conventional ACDF after 5 year follow-up. Long term clinical results comparing full endoscopic anterior cervical discectomy & fusion (ACDF) to conventional ACDF are still needed.

Thoracic Spine Approach

Endoscopy allows surgeons to address thoracic spinal canal pathology such as disc herniations and stenosis directly without significantly destabilization that can occur with open approaches. Fusion of the thoracic spine is not required with endoscopic techniques. Endoscopic transforaminal thoracic discectomy for the treatment of soft disc herniations has demonstrated clinical improvements in VAS and ODI scores after a 5 year follow-up. Thoracic endoscopic techniques are reserved for experienced endoscopic spine surgeons due to the angle of the approach and the sensitivity of working around the thoracic spinal cord.

Lumbar Interbody Fusion

For endoscopic lumbar interbody fusions, the approach angle is similar to the minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) technique. Current indications for endoscopic TLIF are patients with unilateral foraminal stenosis and mild central stenosis. Other endoscopic TLIF techniques avoid removing the ipsilateral facet altogether in patients who will improve with just an indirect decompression. In patients with bilateral foraminal stenosis, severe central stenosis, or high grade spondylolisthesis, unilateral endoscopic lumbar interbody fusion has limited utility.

Biportal Approaches

Most endoscopic techniques taught in the United States are full endoscopic uniportal approaches but biportal endoscopy is used widely in other countries. The biportal endoscopic technique adds another tool to an endoscopic spine surgeon’s armamentarium. UBE has been supported by good surgical results for the treatment of lumbar stenosis and disc herniation and has expanded to biportal extraforaminal and other endoscopic approaches. ^, Studies comparing unilateral biportal endoscopic (UBE) discectomy to open microdiscectomy have showed similar results in postoperative pain control, leg pain, and functional disability. UBE had less operative blood loss, shorter hospital stay and better immediate postoperative back pain. A randomized controlled trial (RCT) published in 2020 compared biportal endoscopic lumbar decompression versus microscopic lumbar decompression and demonstrated equivocal postoperative ODI, EQ-5D, and VAS scores at 12-month follow-up.

Clinical Outcomes in the Lumbar Spine

When considering whether to offer endoscopic spine surgery to patients, a realistic review of the present data is important to consider. A concern amongst already practicing spine surgeons is whether endoscopic techniques are providing real clinical benefit to patients. Are the outcomes worth the investment in time, capital, and learning necessary to implement these techniques? Study results have generally shown that patients are achieving similar improvements in their back and leg pain but with quicker recovery and return to home and work after endoscopic surgery compared to traditional open surgery. This is thought to be due to the minimal paraspinal muscle damage and conservation of bony anatomy during endoscopic approaches. A biomechanical cadaveric study demonstrated that endoscopic transforaminal decompression resulted in a 45.5% increase in foraminal area without axial or extension flexibility changes at the surgical level. Traditional open posterior decompression resulted in a 34% increase in foraminal area with significant increase in extension and axial rotation flexibility.

Several systematic reviews and meta-analyses have determined that endoscopic spine surgery results in good improvements in Visual Analog Scale (VAS) and Oswestry Disability Index (ODI) scores postoperatively. ^, Transforaminal endoscopic discectomy and open microscopic discectomy do not have significant differences in reoperation and complication rates but there is less postoperative back pain, a shorter hospital stay, and faster overall recovery in endoscopic surgery. ^, Several RCTs have demonstrated the clinical success of endoscopic approaches ( Table 1 ). A 2017 RCT of 143 patients demonstrated that transforaminal endoscopic discectomy (TED) had lower affected side leg pain at 2 years compared to microdiscectomy. In addition, hospital stay was significantly shorter in the TED group. An RCT published in 2022 compared TED to conventional open microdiscectomy for patients with at least 6 weeks of radiating leg pain. The study showed that patients randomized to TED had a significantly lower postoperative VAS score for leg pain compared to conventional open microdiscectomy. There was also less blood loss, shorter hospital stays and less back pain in the TED group.

Endoscopic treatment of lumbar stenosis has also demonstrated good clinical outcomes. A 2009 RCT showed that full endoscopic interlaminar decompression had similar clinical outcomes to microsurgical decompression but with significantly lower complication rates and revisions. Endoscopic treatment for multiple levels of lumbar stenosis has been comparable to open surgery. ^,

Compared to tubular minimally invasive techniques, endoscopic lumbar decompression has shown reductions in the hospital length of stay, 1 year postoperative leg pain, and back pain disability.

Clinical Outcomes in the Cervical Spine

In the cervical spine, endoscopic posterior cervical foraminotomies have demonstrated similar outcomes to conventional (ACDF). That RCT noted that the full endoscopic technique had an advantage because it does not require implantation of hardware. Compared to open cervical foraminotomy, endoscopic posterior foraminotomy has the advantage of less blood loss, shorter operative time, and shorter hospital length of stay.

Clinical Outcomes in the Thoracic Spine

Endoscopic interlaminar, extraforaminal, and transthoracic retropleural approaches for the treatment of disc herniations and thoracic stenosis have shown sufficient spinal canal decompression with good clinical results. ^, The extraforaminal approach has a significantly lower complication rate compared to the other 2 thoracic approaches and is the preferred thoracic approach. Since a fusion is not required with thoracic endoscopic approaches, the complications associated with hardware placement are not encountered. Endoscopic resection of calcified disc herniations has been performed but there are limited clinical data on the technique. Unilateral biportal endoscopic techniques for thoracic fusion surgery have been described but are not common practice. As with open thoracic approaches, accuracy with the approach is important to avoid injury to the surrounding vasculature, lungs, ribs, and to limit postoperative neurologic deficits.

Biportal Endoscopic Outcomes

A comparative analysis studied the differences between biportal endoscopy, uniportal endoscopy, and microsurgery for the treatment of lumbar stenosis via bilateral decompression. Microdiscectomy and biportal endoscopy resulted in more significant dural expansion on postoperative MRI compared to uniportal endoscopy. Less facetectomy was required in the biportal endoscopy group compared to the other 2. Immediate postoperative VAS scores for back pain were significantly lower in both endoscopy groups compared to the microsurgical group. Although at final follow-up there were no significant differences in the VAS scores for back pain or leg pain and no difference in ODI for all 3 groups.

When comparing uniportal and biportal endoscopic surgery, both procedures demonstrated similar efficacy but operative time was shorter and central canal decompression was improved in the UBE group. Biportal endoscopic TLIF has shown no significant differences in clinical outcomes compared to conventional MIS-TLIF. ^, There are also no reported differences in early and midterm fusion rates between biportal and uniportal endoscopic fusion.

Open versus Endoscopic Complications

Early studies demonstrated a clinically similar rate of overall complications with endoscopic surgery compared to open spine surgery but more recent analyses have identified some differences. A 2019 retrospective study of 1839 patients showed that overall complications after transforaminal endoscopic discectomy was one magnitude lower than the complication rate for microdiscectomies. A meta analysis of 6 RCTs reported that endoscopic lumbar discectomy had a 50% reduction in overall complications compared to traditional lumbar microdiscectomy. Durotomies are also reportedly decreased in endoscopic surgery. Retrospective survey data of 64,470 lumbar endoscopy cases resulted in 689 dural tears with a durotomy incidence of 1.07%. Intraoperative complications in endoscopic spine surgery will happen more frequently when first starting to learn and practice the techniques. As the surgeon becomes more experienced, the complication rate should decrease and become comparable to similar minimally invasive procedures.

There is a significantly lower risk of surgical site infections (SSI) in endoscopic spine surgery compared to traditional lumbar surgery. A retrospective multicenter cohort study compared 1277 noninstrumented full endoscopic spine surgery (FESS) cases compared to 55,882 nonendoscopic matched cohort patients using the National Surgical Quality Improvement Program (NSQIP) database. In the matched data, the SSI rates for nonendoscopic and endoscopic patients were 1.2% and 0.079%, respectively, a 16 times reduction in endoscopy. This study did not include cases involving trauma, arthrodesis, spine tumors, or greater than 4 levels treated. The SSI rate of traditional lumbar microdiscectomies is already low, but as full endoscopic surgical techniques are applied broadly, the reduction in SSI’s can have a larger clinical effect.

Complications in Difficult Patient Populations

Revision spine surgery has high rates of infections, durotomies, and other intraoperative complications due to surrounding scar tissue and dural adhesions. A transforaminal endoscopic approach is advantageous in this population by approaching through untouched tissue and avoiding scar tissue. A prospective study by Hoogland and colleagues looked at 262 patients who underwent transforaminal endoscopic lumbar discectomy for recurrent disc herniation. At 2 years follow-up, better than 95% of patients reported good outcomes with a 3.8% overall complication rate with no infections or durotomies. Of those patients, 4.7% reported a third recurrent disc herniation.

Obese patients have a higher surgical morbidity risk and provide a challenge during traditional spinal exposure techniques due to the amount of necessary tissue dissection. Endoscopic spine surgery does not require extensive tissue dissection and provides an advantage in obese patients. A study of 41 patients with a body mass index (BMI) greater than 30 kg/m2 who underwent endoscopic lumbar decompression procedures showed that they were able to achieve significant improvements in pain and disability without high rates of blood loss or significant postoperative complications. Mean operative time in patients with a BMI greater than 30 kg/m2 is shorter in endoscopic discectomy patients compared to open microdiscectomy.

Addressing Endoscopic Complications

Patient education regarding spinal endoscopy risks should be covered when offering endoscopic treatment. A 2024 systematic review of complications in endoscopic spine surgery found an incidence rate of 3.1%–7.4% for all perioperative complications not involving fusions. Major complications (epidural hematoma, incomplete decompression, new or continued neurologic deficit, and infection) ranged from 0.8%–1.8%. The highest incidence of minor complications was dysesthesia which ranged from 1.3%–2%. Studies involving endoscopic fusions had higher complication rates with an overall complication rate of 12.3%. Nerve root dysesthesias, most cases being transient, can be frustrating to patients expecting immediate results. Significant and prolonged retraction of the nerve root during endoscopic transforaminal cases leads to higher rates of postoperative transient dysesthesias. Reasonable patient counseling of postoperative expectations is necessary with every case.

In the current literature, most small durotomies are left unrepaired due to the pressure of the surrounding undisturbed tissues used to tamponade the cerebrospinal fluid. Other medium to small sized durotomies can be repaired with a dural or tissue graft and fibrin glue. During biportal techniques, nonpenetrating clips have successfully closed dura but are not used during uniportal cases due to the size of the device. Classic suture closure techniques through an endoscope are difficult but the advancement of dural closure technology is helping make dural repair during endoscopic surgery more feasible.

Navigation Techniques

Current intraoperative endoscopic localization utilizes fluoroscopy for incision planning and confirmation of successful “docking” of the endoscope. Limitations to this include the radiation exposure to the operating room staff and patient and performing localization with 2-dimensional images. Intraoperative navigation technology using an intraoperative computed tomography (CT) scan and 3D image reconstruction could be applied to endoscopic surgery to improve instrument and hardware accuracy.

Robotic Assistance

Navigated intraoperative robotic assistance has been shown to have improved outcomes compared to freehand and fluoroscopic assisted pedicle screw placement techniques. ^, Navigated robot assistance can be used to accurately position an endoscope and then hold the scope in a stable position throughout surgery. It has been used as an assistive tool during endoscopic TLIF’s and as a stable trajectory and depth stop for the endoscope and endoscopic drill. ^,

The Endoscopic Learning Curve

Interest in endoscopic spine surgery continues to grow as evidenced by the increase in yearly publications, but specific endoscopic training is not common in residency or spine fellowship curriculum. Formal training while in practice is limited and interested surgeons are learning at cadaver courses with a day or 2 to practice the various techniques. Previous studies suggest that it takes about 70 cases for training surgeons to produce good clinical results. In the 2022 RCT demonstrating that TED had significant clinical improvements compared to open microdiscectomy, 125 patients in this study were part of the “learning curve” group of surgeons first learning how to perform TED. Surgeons can still have successful outcomes while learning endoscopic techniques. Just as with any spinal procedure, it is important to use anatomic landmarks to stay oriented as damage to the exiting nerve root can lead to postoperative dysesthesia and radiculitis.

Capital Expenditure Barriers, Endoscopic Cost-Effectiveness, and Reimbursement

Starting a successful endoscopic program requires proving to the hospital system that the economic value it brings is worth the initial capital expenditures and startup costs. The initial capital expenditure of endoscopic equipment in North America has been reported in the data to be around $350,000. In our experience, companies provided estimates of initial equipment costs for a fully supported endoscopic system (endoscopes, cameras, monitors, instruments, etc) ranging from $500,000-$800,000. In addition, a study found that per case equipment costs average about 158,000 Yen, equivalent to about $1080. Negotiating for endoscopic equipment that minimizes the use of disposable instruments can help reduce surgical costs per case.

These up front costs can be overcome by the benefits to the individual patient and health care systems due to the reduction in complications associated with surgery. For example, in the Medicare population, surgical site infections are considered “never events” and are not reimbursed to the hospital system. A conservative estimate of the costs of treating a spine surgical site infection is about $16,242-$21,000 per treatment. ^, Each year, approximately 450,000 to 500,000 microdiscectomies are performed in the United States each year, resulting in about 5,500 SSI’s and a cost of about $115,500,000 a year. If 500,000 microdiscectomies are replaced with endoscopic discectomies that would theoretically reduce the number of SSI’s to around 343 cases and a cost reduction in the United States of about $112 million a year. If a hospital performs 100 microdiscectomies and cervical foraminotomies in a year, typically that results in about 1 to 2 infections. With endoscopic spine surgery, 1 SSI occurs with about 1500 cases performed. This is a savings of about $336,000 in that time period. When endoscopic techniques are applied more broadly to laminectomies and fusions, the reduction in infections becomes more significant and further reductions in costs can be seen.

Spinal endoscopy is associated with advantageous health care and societal costs. Compared to microdiscectomy, endoscopic discectomy has about $8,000 difference in costs savings per 1 QALY. Comparing TED to open microdiscectomy for lumbar disc herniation demonstrated that significant postoperative improvement in leg pain and quality-adjusted life years (QALYs) were found in the TED group at 12 months. Surgical costs were higher for TED compared to open microdiscectomy but TED was found to be more cost effective overall when quantifying its societal cost benefits. Faster hospital discharges and a reduction in overall complications reduce costs per patient but depending on surgical volume, it may take years before the initial investment costs are overcome.

Insurance approval for endoscopic cases is difficult and there are strict requirements for proving the indications for endoscopic treatments. Determining the best way to quantify reimbursement has also been difficult. The first Current Procedural Terminology (CPT) code (number 62380) for endoscopic spine surgery was first released in 2017. This code covers only lumbar endoscopic decompression of the spinal cord but does not differentiate between different types of decompression or if a discectomy is performed. Suggestions to alter the reimbursement coding have included adding an endoscopic “add on” option to already present CPT codes for cases such as posterior cervical foraminotomy and discectomy.

Indications and Their Limitations

Current common endoscopic surgical indications include lumbar disc herniations and lumbar stenosis, treated either by interlaminar or transforaminal approaches. As surgical experience increases, cervical foraminal stenosis from anterior or posterior compression can be treated with endoscopic posterior cervical foraminotomy. As an endoscopic spine surgeon gains considerable expertise, thoracic disc herniations can be approached transforaminally. Variations of these techniques, such as the trans-superior articular process (Trans-SAP) approach or posterior cervical laminectomies can also be employed by the expert endoscopic spine surgeon. Pathology requiring treatment of greater than 3 levels or deformity correction is not currently recommended in the literature.

Spinal neoplasms are not commonly treated endoscopically. Case reports have demonstrated the feasibility of endoscopic techniques to treat osseous lesions of the spine and extradural tumors. ^, Others have described endoscopic resection of intradural tumors but note how technically demanding the procedures are. Due to significant tissue loss with continuous irrigation and narrow tissue exposure, endoscopic resection of tumors is typically limited to benign lesions. There is insufficient quality of evidence to definitively recommend endoscopic resection of spinal neoplasms and high quality data are needed.

The endoscopic management of spinal infections. Endoscopic debridement of spondylodiscitis demonstrated a 54.2%–90% success rate with microorganism identification but also a high potential treatment failure rate of 33%. A retrospective review of 20 patients undergoing endoscopic debridement and drainage of surgical infections after lumbar instrumented fusion demonstrated an 85% rate of successful bacterial identification and 65% infection control. Due to the inconsistent extent of scar present from spinal infections, a high variability of surgical difficulty can occur during endoscopic treatment. Surgeons should have a keen sense of when to convert to open debridement if needed.